Which situation is a valid reason to abort a start?

The scenario where there is a "hot, hung, no, bat bus light goes out" is a valid reason to abort a start because it indicates critical issues with the engine start sequence and electrical system. A "hot" start refers to an engine that has ignited but is producing excessive temperatures, while a "hung" start refers to the situation where the engine fails to accelerate properly during the start process, possibly leading to damage. The "no bat bus light goes out" indicates that there may be issues with the battery or electrical bus that could jeopardize the engine's operation and overall aircraft systems.

In aviation, safety is paramount, and recognizing these indicators suggests the potential for malfunction or failure, necessitating an immediate abort of the start to avoid further complications and protect both the aircraft and crew. This aligns with standard operating procedures that prioritize ensuring systems are functioning correctly before completing a start sequence.

The other choices do not present as direct and immediate threats that require an abort. External temperature fluctuations might affect performance but don't directly necessitate aborting the start. Battery power at maximum capacity is not inherently a reason for concern. If the "bat bus light" is functioning as expected, it's not indicative of a failure either, making it less critical